A heat-sensitive recording material is generally one obtained by separately dispersing a colorless or light color leuco-dye and a developer such as a phenolic material or the like in the form of fine particles, then mixing the two, adding thereto additives such as a binder, a sensitizer, a filler, a lubricant and the like to form a coating solution and then applying the coating solution to paper, a film, a synthetic paper or the like, and one or both of the leuco-dye and the developer are melted by heating and the two are contacted to cause a chemical reaction, thereby obtaining a developed record. For developing this heat-sensitive recording sheet, a thermal printer or the like having a built-in thermal head is used. This heat-sensitive recording method has such characteristics that as compared with other recording methods, (1) no noise is caused during recording, (2) development, fixing and the like are not required, (3) maintenance is unnecessary, (4) the machine is relatively inexpensive and the like, and hence, is widely used in the facsimile field, the field of printer for computer output, electronic calculator and the like, the field of recorder for medical measurement, the automatic ticket vending machine field, the heat-sensitive recording type label field and the like.
Recently, with the POS systemization in a retail store, a supermarket and the like and the automatization of the system of traffic facilities, the application of heat-sensitive recording materials to labels, tickets, coupon tickets and the like increases. In these applications, it has been desired that the heat-sensitive recording material has a much more improved preservation stability. In addition, a demand for high speed recording has become higher and the development of a heat-sensitive recording material capable of sufficiently responding to the high speed recording has been strongly desired. However, in general, when the sensitivity of a heat-sensitive recording material is heightened to make the heat-responsibility good, such a disadvantage that Discoloration of the ground is caused becomes easy to cause. As to heat-sensitive recording materials in which 3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone which is an example of the bisphenol S derivative is used as a developer, many patents have been applied for. They include, for example, JP-A-60-208,286, JP-A-61-89,090, JP-A-61-199,985, JP-A-61-199,986, JP-A-61-199,987, JP-A-61-199,988, JP-A-61-228,985, JP-A-62-53,957, JP-A-63-3,988, JP-A-1-67,380, JP-A-1-150,576, JP-A-1-178,491 and the like. Among them, those describing a method for preparing 3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone are two of JP-A-61-89,090 and JP-A-62-53,957. However, even when 3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone prepared according to the methods described therein is used, the recent high requirement for the Discoloration of the ground in heat and moisture has not been satisfied though the enhancement of preservation stability is improved to some extent.